An inflator for inflating a vehicle occupant protection device, such as an air bag, contains a body of ignitable gas generating material. The inflator further includes an igniter. The igniter is actuated so as to ignite the body of gas generating material when the vehicle experiences a condition, such as a sudden deceleration, which is indicative of a collision for which inflation of the air bag is desired. As the body of gas generating material burns, it generates a volume of inflation gas. The inflation gas is directed into the vehicle air bag to inflate the air bag. When the air bag is inflated, it expands into the vehicle occupant compartment and helps to protect the vehicle occupant.
The body of gas generating material comprises a gas generating composition. One useful oxidizer for gas generating compositions for a vehicle occupant protection device is ammonium nitrate. Gas generating compositions comprising an energetic fuel and ammonium nitrate as the oxidizer can provide a clean, smokeless burn. However, such compositions generally have poor ignition properties and a low burn rate. To achieve higher ignition and burn rates, the inflator has to be operated at a high pressure and has to use a body of gas generating material having a large surface area, such as is provided by a large quantity of small tablets.